In traditional film/screen medical diagnostic imaging, an anatomical part of a patient is positioned between an x-ray source and an unexposed film/screen, an x-ray exposure of the anatomical part produces a latent x-ray image in the film and the film is developed. The developed x-ray film is then viewed on a light box by a diagnostician (radiologist/physician). More recently, medical diagnostic imaging modalities, such as CT and MRI scanners, have produced video x-ray images which are viewed on a video monitor. Frequently, a permanent x-ray image of a video x-ray image is made by photographing the video monitor to produce an x-ray film image. The x-ray film image can also be produced by a laser printer (such as the KODAK EKTASCAN LASER PRINTER sold by the Eastman Kodak Company, Rochester, N.Y.).
When using a laser printer to produce a permanent x-ray film image, problems arise from the different video formats used by different medical imaging modalities. Typically, the analog video signal produced by the modality is converted to a digital image signal which is used to drive the laser printer.
Because some incoming video formats lack serrating pulses during the vertical sync time interval, when a phase-locked-loop (PLL) is used as a frequency synthesizer to recover a pixel clock from a composite video signal, the clock recovery circuitry will lose lock if no serrating pulses are present. The signal compensating and PLL circuits disclosed in the following patents are not entirely suitable for such applications.
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